Re: [RFC PATCH v4 00/17] virtio/vsock: introduce SOCK_SEQPACKET support

[Stefano Garzarella]

Hi Arseny,

On Mon, Feb 08, 2021 at 09:32:59AM +0300, Arseny Krasnov wrote:
> On 07.02.2021 19:20, Michael S. Tsirkin wrote:
> > On Sun, Feb 07, 2021 at 06:12:56PM +0300, Arseny Krasnov wrote:
> > > 	This patchset impelements support of SOCK_SEQPACKET for virtio
> > > transport.
> > > 	As SOCK_SEQPACKET guarantees to save record boundaries, so to
> > > do it, two new packet operations were added: first for start of record
> > >  and second to mark end of record(SEQ_BEGIN and SEQ_END later). Also,
> > > both operations carries metadata - to maintain boundaries and payload
> > > integrity. Metadata is introduced by adding special header with two
> > > fields - message count and message length:
> > >
> > > 	struct virtio_vsock_seq_hdr {
> > > 		__le32  msg_cnt;
> > > 		__le32  msg_len;
> > > 	} __attribute__((packed));
> > >
> > > 	This header is transmitted as payload of SEQ_BEGIN and SEQ_END
> > > packets(buffer of second virtio descriptor in chain) in the same way as
> > > data transmitted in RW packets. Payload was chosen as buffer for this
> > > header to avoid touching first virtio buffer which carries header of
> > > packet, because someone could check that size of this buffer is equal
> > > to size of packet header. To send record, packet with start marker is
> > > sent first(it's header contains length of record and counter), then
> > > counter is incremented and all data is sent as usual 'RW' packets and
> > > finally SEQ_END is sent(it also carries counter of message, which is
> > > counter of SEQ_BEGIN + 1), also after sedning SEQ_END counter is
> > > incremented again. On receiver's side, length of record is known from
> > > packet with start record marker. To check that no packets were dropped
> > > by transport, counters of two sequential SEQ_BEGIN and SEQ_END are
> > > checked(counter of SEQ_END must be bigger that counter of SEQ_BEGIN by
> > > 1) and length of data between two markers is compared to length in
> > > SEQ_BEGIN header.
> > > 	Now as  packets of one socket are not reordered neither on
> > > vsock nor on vhost transport layers, such markers allows to restore
> > > original record on receiver's side. If user's buffer is smaller that
> > > record length, when all out of size data is dropped.
> > > 	Maximum length of datagram is not limited as in stream socket,
> > > because same credit logic is used. Difference with stream socket is
> > > that user is not woken up until whole record is received or error
> > > occurred. Implementation also supports 'MSG_EOR' and 'MSG_TRUNC' flags.
> > > 	Tests also implemented.
> > >
> > >  Arseny Krasnov (17):
> > >   af_vsock: update functions for connectible socket
> > >   af_vsock: separate wait data loop
> > >   af_vsock: separate receive data loop
> > >   af_vsock: implement SEQPACKET receive loop
> > >   af_vsock: separate wait space loop
> > >   af_vsock: implement send logic for SEQPACKET
> > >   af_vsock: rest of SEQPACKET support
> > >   af_vsock: update comments for stream sockets
> > >   virtio/vsock: dequeue callback for SOCK_SEQPACKET
> > >   virtio/vsock: fetch length for SEQPACKET record
> > >   virtio/vsock: add SEQPACKET receive logic
> > >   virtio/vsock: rest of SOCK_SEQPACKET support
> > >   virtio/vsock: setup SEQPACKET ops for transport
> > >   vhost/vsock: setup SEQPACKET ops for transport
> > >   vsock_test: add SOCK_SEQPACKET tests
> > >   loopback/vsock: setup SEQPACKET ops for transport
> > >   virtio/vsock: simplify credit update function API
> > >
> > >  drivers/vhost/vsock.c                   |   8 +-
> > >  include/linux/virtio_vsock.h            |  15 +
> > >  include/net/af_vsock.h                  |   9 +
> > >  include/uapi/linux/virtio_vsock.h       |  16 +
> > >  net/vmw_vsock/af_vsock.c                | 588 +++++++++++++++-------
> > >  net/vmw_vsock/virtio_transport.c        |   5 +
> > >  net/vmw_vsock/virtio_transport_common.c | 316 ++++++++++--
> > >  net/vmw_vsock/vsock_loopback.c          |   5 +
> > >  tools/testing/vsock/util.c              |  32 +-
> > >  tools/testing/vsock/util.h              |   3 +
> > >  tools/testing/vsock/vsock_test.c        | 126 +++++
> > >  11 files changed, 895 insertions(+), 228 deletions(-)
> > >
> > >  TODO:
> > >  - What to do, when server doesn't support SOCK_SEQPACKET. In current
> > >    implementation RST is replied in the same way when listening port
> > >    is not found. I think that current RST is enough,because case when
> > >    server doesn't support SEQ_PACKET is same when listener missed(e.g.
> > >    no listener in both cases).

I think is fine.

> >    - virtio spec patch
> Ok

Yes, please prepare a patch to discuss the VIRTIO spec changes.

For example for 'virtio_vsock_seq_hdr', I left a comment about 'msg_cnt' 
naming that should be better to discuss with virtio guys.

Anyway, I reviewed this series and I left some comments.
I think we are in a good shape :-)

Thanks,
Stefano